Effects of phase-locked-loop circuit on a self-commutated BTB system under line faults

Abstract

A self-commutated BTB (Back-To-Back) system is an ac-dc-ac power flow controller between two utility grids, and PLL (Phase-Locked-Loop) circuits are typically used for detecting their phase information. The performance of the BTB system during line faults is strongly affected by the dynamic behavior of the PLL circuit in terms of the ac-current fluctuation, the dc-voltage fluctuation, and the dc magnetic flux deviation in the converter-transformers. However, no paper or article has been discussed explicitly on their mutual relationship. The aim of this paper is to establish a design procedure of the PLL circuit which is suitable for the BTB system. This paper also deals with the dc magnetic flux deviation in the converter-transformers under double-line-to-ground (DLG) faults.Keywords -BTB (Back-to-Back) systems, power flow control, DLG fault, dc magnetic flux deviation, PLL (Phase-Locked-Loop) circuit.

Low-voltage-ride-through (LVRT) capability of a phase-shifted-PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC)

“…3(c) depicts the situation when a two-phase, also known as doubleline, sag with a depth of 100% occurs. As can be seen, the imbalance caused by the absence of one or two phase voltages brings a displacement of the ac power supply unit line-to-line voltages, which is known consequently as the so-called "phase jump" [12]. When a three-phase voltage sag with a depth of 100% occurs, no voltage is present in the three-phase ac power supply unit terminals, as shown in Fig.…”

“…Control block diagram.caused by the imbalanced three-phase ac mains voltages. A 100-Hz ac component becomes present on the dq reference frames voltages v Sd and v Sq[12]. To avoid the failure of synchronization with the ac power supply units, the loop filter of the PLL is designed to suppress the 100-Hz component present in the voltage v Sq .…”